The present invention relates to a technique for detecting a receiving signal in radio communication using code division multiple access (CDMA), more particularly, to an apparatus and method for adaptive CDMA detection based on constrained minimum mean squared error criterion.
A typical adaptive Minimum Mean Squared Error (MMSE) apparatus for detecting a receiving signal has a good performance in a fixed channel environment and a simple structure, while its performance is severely degraded in a fading channel environment. This is due to the fact that the adaptive filter cannot be adapted to the rapid change of a channel phase and amplitude.
There are several methods to solve the problem. Some techniques of the methods have been proposed in articles, for example, S. L. Miller and A. N. Barbosa, xe2x80x9cA modified MMSE Receiver for Detection of DS-COMA Signals in Fading Channelsxe2x80x9d, Proc.MILCOM""96, pp.898-902; and M. Latva-abo and M. Juntti, xe2x80x9cModified Adaptive LMMSE Receiver for DS-CDMA Systems in Fading Channelsxe2x80x9d, Proc.PIMRC""97, pp.554-558.
The first technique relates to reducing the channel load by compensating a phase variation component of channel for an input signal of an adaptive filter. But, since the method compensates only a phase component of channel, the performance of the adaptive filter decreases in case of a large variation of an amplitude component of channel.
The second technique relates to simultaneously compensating a phase and amplitude for a reference signal for an adaptive filter. In this case, using an input signal of the adaptive filter included in a component of Multiple Access Interference (MAI) performs the channel estimation for compensation. If the channel is estimated by using a MAL removed input signal of adaptive filter and a phase and amplitude are compensated by the channel estimation, as described FIG. 4 (see A in FIG. 4), all the tap weights of the adaptive filter converge to zero. Thus, the receiving apparatus cannot be operated.
Accordingly, an apparatus in which a channel is estimated by using an output signal of an adaptive filter, and a phase and amplitude are compensated by the channel estimation, a tap weight of an adaptive does not converge to zero, and operates normally is requested.
The object of the present invention is to provide an adaptive apparatus for detecting a receiving signal employing constrained minimum mean square error (MMSE) criterion as an adaptive algorithm for detecting a receiving signal in CDMA system, in which an adaptive filter can be normally operated even if compensating a phase and amplitude of a channel at the same time.
Also, the present invention is to provide an adaptive method for detecting a receiving signal employing constrained minimum mean square error (MMSE) criterion as an adaptive algorithm for detecting a receiving signal CDMA system, in which an adaptive filter can be normally operated even if compensating a phase and amplitude of a channel at the same time.
Further, the present invention is to provide a recording media for implementing an adaptive method for detecting a receiving signal employing constrained minimum mean square error (MMSE) criterion as an adaptive algorithm for detecting a receiving signal in CDMA system, in which an adaptive filter can be normally operated even if compensating a phase and amplitude of a channel at the same time.
To accomplish the objects, the present invention provides an adaptive apparatus for detecting a receiving signal in CDMA communication system comprising: an adaptive filtering means for filtering a complex receiving signal according to a tap weight controlled by a predetermined period; a channel estimating means for estimating a phase component and a amplitude component of a particular user channel by using the output signal of the adaptive filtering means; a signal restoring means for restoring an original signal transmitted from the particular user by using the channel estimated signal from the channel estimating means and the filtered receiving signal from the adaptive filtering means; a selecting means for selecting and providing either the restored signal from the signal restoring means or a known training signal; a reference signal generating means for generating a reference signal by using the channel estimated signal from the channel estimating means and the selected signal from the selecting means; an error calculating means for calculating an error between the filtered receiving signal from the adaptive filtering means and the reference signal from the reference signal generating means by comparing the signals; and a tap weight controlling means for controlling the tap weight of the adaptive filtering means based on constrained minimum mean square error(MMSE) criterion.
Also, the present invention provides an adaptive method for detecting a receiving signal in CDMA communication system comprising the steps of: a first step for removing an interference signal from a receiving signal according to a tap weight of an adaptive filter controlled by a predetermined period; a second step for estimating a phase component and a amplitude component of a particular user channel by using the filtered complex receiving signal; a third step for restoring an original signal transmitted from the particular user from the filtered complex receiving signal by using the channel estimated value from the second step, wherein the filtered complex receiving signal is estimated as a receiving signal transmitted from the particular user; a forth step for selecting and providing either the restored signal from the third step or a known training signal; a fifth step for generating a reference signal by using the channel estimated signal from the second step and the selected signal from the forth step; a sixth step for calculating an error between the filtered complex receiving signal and the reference signal by comparing the signals; and a seventh step for re-establishing the tap weight of the adaptive filtering means based on constrained minimum mean square error(MMSE) criterion, then iterating the steps from the first step.
And, the second step comprises the steps of: a pilot signal extracting step for extracting a known pilot signal with a predetermined period included in the filtered receiving signal from the first step; a first operating step for multiplying the pilot signal by a predetermined value; a second operating step for adding all the output value of the first operating step in a predetermined period; a third operating step for finding and outputting the mean by dividing the sum of the second operating step into the number of output value of the first operating step.
And, the third step comprises the steps of: a forth operating step for multiplying the output signal of the second step by the output signal of the first step; a real value extracting step for extracting a real component from the output value of the forth step; and a bit value determining step for determining a bit value of the extracted real value from the real value extracting step.
And, the sevenths step comprises the steps of: a pseudo noise(PN) generating step for providing a pseudo noise(PN); a fifth operating step for multiplying the receiving signal by the PN signal; a sixth operating step for multiplying the output signal of the fifth operating step by the PN signal; a seventh operating step for subtracting the output signal of the sixth operating step from the receiving signal; a eighth operating step for multiplying the complex conjugate of the error signal from the sixth operating step by the output signal of the seventh operating step; a ninth operating step for multiplying the step size determining the controlling period of the tap weight by the output signal of the eighth operating step; a tenth operating step for adding an operated output signal immediately before to the output signal of the ninth operating step; a eleventh operation step for adding the PN signal to the output signal of the tenth operating step, and establishing the sum as a new tap weight of the adaptive filter.
Further, the present invention provides a recording media read by a computer, in which is recorded with a program for implementing functions in an adaptive apparatus for detecting a receiving signal in CDMA communication system including a processor, the functions comprising: a first function for removing an interference signal from a receiving signal according to a tap weight of an adaptive filter controlled by a predetermined period; a second function for estimating a phase component and a amplitude component of a particular user channel by using the filtered complex receiving signal; a third function for restoring an original signal transmitted from the particular user from the filtered complex receiving signal by using the channel estimated value of the second function, wherein the filtered complex receiving signal is estimated as a receiving signal transmitted from the particular user; a forth function for selecting and providing either the restored signal by the third function or a known training signal; a fifth function for generating a reference signal by using the channel estimated signal performed by the second function and the selected signal by the forth function; a sixth function for calculating an error between the filtered complex receiving signal and the reference signal by comparing the signals; and a seventh function for re-establishing the tap weight of the adaptive filter based on constrained minimum mean square error(MMSE) criterion, then iterating the functions from the first function.